In modern internal combustion engines having reciprocating pistons in cylinders driven by combustion of a mixture of fuel and air, there has, in recent years, been a development toward the use of lower fuel to air ratio of the mixtures or so-called leaner mixtures. The ideal fuel-air mixture is a so-called stoechiometric mixture which has a ratio of fuel to air, such that complete combustion of the fuel is attained. Under this condition, there is a minimum of undesirable polluting by-products, which, in turns, leads to a combustion with the highest possible degree of fuel efficiency.
The leaner mixture, however, suffers from the drawbacks that it is difficult to ignite and that the flamefront of the burning air mass moves through the fuel-air mixture at lower speeds.
In addition, during operation at reduced power and especially during idling, the fuel-air mixture is of very low pressure and also, for that reason, difficult to ignite. In present engines, additional fuel is supplied to the fuel-air mixture during idling. That additional fuel not only causes loss and increased pollution, but also causes increased engine wear. The present invention makes it possible to ignite and burn such a low pressure, lean mixture without additional fuel enrichment.
For those reasons, engine designers have introduced various means to improve the ignition process, such as the provision of multiple spark plugs, more powerful sparks of longer duration, the provision of a separate combustion chamber with a separate intake valve and carburetor and where the ignition is started by means of a small amount of a richer mixture. A version of an ignition system providing more powerful sparks of longer duration, is described in copending application entitled Ignition with Power Boosting Arrangement, application Ser. No. 265,669.
It stands to reason, and can be shown, that a spark plug providing a spark of longer duration will not have much benefit, unless the fuel-air mixture is in motion during the time of ignition so that a larger amount of fuel-air mixture is exposed to the spark during the ignition time.
Various inventors have proposed combustion chambers of such a construction that a swirling motion is imparted to the fuel-air mixture during both the intake cycle and during the compression cycle, in order to provide a better combustion.
An example of an internal combustion engine having a specially constructed combustion chamber and piston which provides additional swirling motion of the fuel-air mixture, is described in U.S. Pat. No. 4,026,250, issued Mar. 13, 1979. Another example of such an engine is described in U.S. Pat. No. 4,280,459, granted July 28, 1981.
The present invention discloses a special construction of a combustion chamber with a corresponding piston, which provides an especially strong swirling motion of the fuel-air mixture at the time of ignition, and such that the swirling fuel-air mass can be directed toward the spark gap of the spark plug. By further providing an ignition system which delivers a powerful spark of appropriately extended duration, a highly efficient combustion of a lean fuel-air mixture can be attained.
The swirling motion imparted to the fuel-air mixture by the present invention provides the additional beneficial effect that a more intimate and homogeneous fuel-air mixture is attained, which further enhances the quality of the combustion process.
The problems described above, relating to the use of a lean fuel-air mixture are exacerbated by the fact that modern internal combustion engines are required to operate at increasingly higher rotational speeds, in order to attain weight and space reductions of the engine which is required in the overall effort to improve fuel efficiency.
It is, therefore, an important object of the present invention to provide a piston and combustion chamber for an internal combustion engine such constructed that a more complete combustion is attained.
It is another important object of the present invention to provide a piston and combustion chamber for an internal combustion engine that is capable of igniting and burning a lean fuel-air mixture.
It is another important object of the present invention to provide a piston and combustion chamber for an internal combustion engine such constructed that a cleaner combustion with fewer polluting combustion by-products is attained.
It is still another object of the present invention to provide a piston and combustion chamber of such a construction that a more complete and cleaner combustion is attained for an engine operating at a high speed of rotation.
It is still another object of the invention to provide a piston and combustion chamber of such a construction that there is less tendency to engine knocking from premature ignition.
It is still another object of the present invention to provide a piston and combustion chamber of such a construction that the aforesaid objects are attained with a construction that is simple and robust, without the use of additional construction parts.